1. Field of the Invention
The present invention relates to monolithic capacitors having internal electrodes composed of base metals, which are suitable for middle- to high-voltage use requiring a high withstand voltage.
2. Description of the Related Art
Recently, surface mounting of electronic units has been in progress to satisfy the miniaturization of electronic device. As a result more compact electronic units have been used making it necessary to prove more compact monolithic capacitors with higher capacitance.
On the other hand, middle- to high-voltage capacitors with high withstand voltage have been used, for example, in back lights and switching power sources of liquid crystal displays. Requirements for such middle- to high-voltage capacitors are high withstand voltage, further miniaturization, and inexpensiveness.
In conventional middle- to high-voltage monolithic capacitors, suppression of discharge from the outer surfaces of the capacitors is an essential factor for achieving high withstand voltage. Various types of monolithic capacitors having high withstand voltage have been disclosed in, for example, Japanese Utility Model Application Laid-Open Nos. 60-76028, 62-120333, and 58-56431, and Japanese Patent Application Laid-Open No. 62-210612.
For example, in a proposed middle- to high-voltage monolithic capacitor with high withstand voltage, thick ceramic layers are provided above and below the capacitance extraction section composed of a plurality of overlapping internal electrodes, in order to suppress discharge from the top and bottom faces of a sintered ceramic body.
Japanese Patent Application Laid-Open No. 62-210612 discloses a monolithic capacitor with high withstand voltage in which ceramic layers with a relatively low dielectric constant are disposed above and below the capacitance extraction section including overlapping internal electrodes. The ceramic layers suppress flashover above and below the sintered body.
In these conventional middle- to high-voltage monolithic capacitors, thick ceramic layers are disposed above and below the capacitance extraction section; hence the monolithic capacitors are inevitably large, and do not satisfy the requirement for miniaturization and particularly lower heights.
Since these monolithic capacitors and a middle- to high-voltage monolithic capacitor disclosed in Japanese Patent Application Laid-Open No. 62-210612 have internal electrodes composed of noble metals, such as silver and silver-palladium, these are disadvantageous with regard to material costs.
On the other hand, conventional monolithic capacitor configurations capable of reducing material costs use base metals, such as nickel and copper, as internal electrode materials. Since base metals are readily oxidizable, a ceramic material having high reduction-resistant characteristics must be used in the production of monolithic capacitors by a monolithic ceramic firing technology. All the conventional monolithic capacitors are not suitable for middle- to high-voltage use and the ceramic materials used in these monolithic capacitors do not have high reduction-resistant characteristics capable of enhancing withstand voltage.